Replace Broken Glass the Professional Way

Dear James: My three sons always seem to be throwing a ball or something that breaks our windows. Instead of calling a repairman, I would like to save money and do it myself. What is the proper way to replace a pane of glass in a wood window? — Angelo P.

Dear Angelo: Anyone can replace a broken pane of glass in a window, but very few people do it properly. It is fairly easy to spot a nonprofessional job. The putty is usually not applied smoothly and it is not painted properly. Also, without preparing the wood window frame first, the putty will begin to dry out prematurely and crack.

You cannot be too careful when removing the old broken window glass. Always wear work gloves, long sleeves and leather shoes. When you start pulling on the old broken pieces of glass to remove them, they often break and fall to the floor.

Don’t try to remove more than one broken piece of glass at a time, even if they are very small pieces. Wiggle each one before pulling it out of the old putty to make sure that there is not a hidden crack.

If the glass has only one crack across it, you must remove almost all the putty first to remove the two pieces. Old putty can be hard and difficult to chisel out. Warming the putty with a heat gun, hair dryer or soldering iron makes it more flexible. Remove it in small pieces or it may pull some of the wood with it.

It is important to remove all of the old putty after the glass is out. Make sure you do not miss any of the glazier’s points (small triangle that hold the glass pane in place). Run the chisel over the wood to smooth out any rough spots and high points.

Take a small paintbrush and apply a heavy coating of white pure linseed oil on the wood window sash frame where the putty will contact it. Don’t be afraid to saturate the wood with it. The linseed oil will keep the new putty from drying out as fast. This will make it last years longer before the putty cracks and requires replacement.

Lay a very thin, about 1/16 inch, layer of putty in the window frame where the glass pane will rest. Most people forget this first step. Make sure that the glass pane is the correct size. It should be just slightly smaller than its seat in the window frame. Cut it with the glasscutter if necessary.

Press the new pane in firmly against the thin layer of putty. Look at it to make sure that there are no air pockets in the putty. Insert the glazier points around the pane (about every 4 inches) to position and hold it in place. It does not take much force to insert glazier points.

Knead the putty until it is pliable and free of lumps. Roll it in your hands and start in one corner laying it over the glass. When it is all in place, hold the putty knife at an angle and smooth out the putty. Dipping the knife in linseed oil will make it slide easier. Do not spread it out too far, or it will be visible from the other side.

Read the painting instructions on the putty can. Some can be painted immediately and others cannot. Two coats of paint are best. Let the paint flow on to the glass a little to ensure that all of the putty is covered. The dried paint is easy to scrape off the glass.

Send your questions to Here’s How, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com.